Sir Kim’s tone also appears to have shifted since warning Trump was “an outsider and an unknown quantity” in a leaked Downing Street memo.

In an editorial in the Washington Post, the diplomat states the pair have discussed “building on the legacy” of Thatcher and Reagan in the 1980s. He wrote:

“In their phone calls so far, Trump and British Prime Minister Theresa May have made clear that the special relationship between Britain and the United States is stronger than ever.

“They will work together closely, building on the legacy of previous leaders such as President Reagan and Prime Minister Margaret Thatcher.”

STR New / Reuters
Former US President Ronald Reagan (L) greets former British Prime Minister Margaret Thatcher.

He said Britain and the US will work “ever more closely on trade and security” and the UK “remains America’s closest partner on defence”.

“There is much that the United States and Britain should, and will, tackle together as they have for 200 years.

“For decades, our partnership has been the cornerstone of the world order. So we, as an alliance, will continue to be strong.

“2016 was the year that voters in both countries spoke loudly and clearly. 2017 will be the year we show we were listening.”

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Sir Kim Darroch.

In his memo on November 9, leaked to The Sunday Times, Sir Kim told the Prime Minister that “Trump did the apparently impossible” in winning the White House.

“It bears repeating that this soon to be President-elect is above all an outsider and an unknown quantity, whose campaign pronouncements may reveal his instincts, but will surely evolve and, particularly, be open to outside influence if pitched right.”